I've understood that it's ok plus or minus 500 years or so. But then I read the following:

Aged Dated Sherry – Since the year 2000, the controlling board of the D.O. Jerez, known as the Consejo Regulador, has approved a category of 20 and 30 year old certified wines. To become certified, the sherries have to go through a lengthy approval process which is carried out by an independent panel of Sherry experts. Among other requirements, a carbon dating sample is taken to ensure that the youngest molecules of wine in a given solera exceed the 20 or 30 year old age minimum.

Carbon dating is much more accurate than 500 years. Without Googling for specifiics, I believe the Shroud of Tourin was dated within 50 years and artifacts from around 1200 BC are within 100 years. Here's how it works. The normal isotope of carbon has an atomic weight of 12. The normal isotope of nitrogen is 14. When radiation from the sun hits the atmosphere, a certain, consistent amount of the nitrogen looses an electron and one of its protons converts to a neutron, thus producing carbon 14. The amount produced is relatively constant, so there is always the same amount in the atmosphere. This carbon becomes part of all living things in the same proportion to the carbon 12. However, when the living thing dies, it no longer obtains carbon 14, which then decays at a constant rate. I don't recall the half-life, but I believe carbon dating is not useful for more than a few thousand years. By simply measuring the ratio of carbon 14 to carbon 12, one can determine when the object died. The closer to the present, the more accurate. However, contamination can occur, making results less dependable.

Bob Ross wrote:I've understood that it's ok plus or minus 500 years or so. But then I read the following:

Carbon dating became far more accurate when it was calibrated using tree ring samples from bristlecone pines, extending us back ~15,000 years. What was found was the the 12C/14C ratio was not constant with time, but varied, thus causing previous radioisotope dates to be reconsidered. The upshot: carbon dating from the past 10,000 years should be accurate to within a few years; going back further than that, it'll be less accurate.

The dating of recent samples was muddied somewhat (a lot) in the '50's when all and sundry were letting off atomic bombs in the atmosphere. I don't know if this makes dating of stuff from the last 50 odd years more or less accurate that prior to the bomb era.

From another source, the half life of C-14 is 5,730 years approximately, so here is another source of error. The scientists themselves don't know what figures to use.

Cheers,
Neil Courtney

'Wine improves with age. The older I get, the better I like it.' --- Anonymous.

Neil Courtney wrote:The dating of recent samples was muddied somewhat (a lot) in the '50's when all and sundry were letting off atomic bombs in the atmosphere. I don't know if this makes dating of stuff from the last 50 odd years more or less accurate that prior to the bomb era.

From another source, the half life of C-14 is 5,730 years approximately, so here is another source of error. The scientists themselves don't know what figures to use.

No, the figures are known. The number you quote is the "Cambridge" half-life and is the accepted figure now, but many carbon daters use the older number for purely historical reasons. And you're right about the increased 14C in the N. hemisphere from atmospheric A-bomb tests, but that's accounted for in the calibration curves.

Pretty impressive. I can't imagine many other non-physics sites out there where 1) someone asks a question about carbon-14 dating, that 2) draws a bunch of serious and knowledgeable replies. Robin, where did you get these guys? And what do they know about wine?

A lot! Seriously, Dan, I think what we're seeing here is that geeks are geeks. It's no surprise that a lot of people who are seriously into wine are also seriously into science, both as a profession and an obsession. A better questions is how I ended up in this group ... I was an English major.

Bob, You have received lots of excellent responses to your question. To add just a bit of information; C-14 is used in conjunction with other naturally occuring isotopes (potassium) to date materials very accurately, within 20 to 30 years. I also understand that if the geographic origin is known, corrections can be made to date "recent" materials within a few years. Of course any good creationist will be able to tell you all the imagined shortcomings of radio-carbon dating.

Sam

"The biggest problem most people have is that they think they shouldn't have any." - Tony Robbins

Bob, Sorry for posting twice. Itchy trigger finger after a couple weeks of vacation. Don't discount the possibility that God made the sherry to appear old just because he felt like it. I'm sure that sherry aging is right at the top of his priority list just now. Oops! Just heard a clap of thunder!

Sam

"The biggest problem most people have is that they think they shouldn't have any." - Tony Robbins

It would be nearly impossible to Carbon Date a 20-30 year old sample, given that the half-life is over 5000 years. It would require that one be able to differentiate a probability of .994 from .996 within experimental error.

Sam Platt wrote:Bob, Sorry for posting twice. Itchy trigger finger after a couple weeks of vacation. Don't discount the possibility that God made the sherry to appear old just because he felt like it. I'm sure that sherry aging is right at the top of his priority list just now. Oops! Just heard a clap of thunder!

I was reading over some information about radiocarbon dating in the following link and it seems to indicate that trying to age anything in the 20th century is useless because of the influx of fossil carbon into the atmosphere in the past 100 years:

But as the method was refined, it started to show rather regular anomalies. First, it was noticed that, when radiocarbon dated, wood grown in the 20th century appears more ancient than wood grown in the 19th century. Suess explained the phenomenon by the fact that the increased industrial use of fossil carbon in coal and in oil changed the ratio between the dead carbon C12 and the C14 (radiocarbon) in the atmosphere and therefore also in the biosphere. In centuries to come a body of a man or animal who lived and died in the 20th century would appear paradoxically of greater age since death than the body of a man or animal of the 19th century, and if the process of industrial use of fossil, therefore dead, carbon continues to increase, as it is expected will be the case, the paradox will continue into the forthcoming centuries.

Howie, Creationists love Velikovsky and his writings. His focus was on "interpreting" archeological, and cosmological data to prove that the events described in the bible are literally true and accurate. To do so he had to play play fast and loose with well established scientific principles and well documented events in world history. Which he did with wreckless abandon. As a psuedoacademic he was dismissed by his peers after which he claimed a conspiracy to prevent him from getting his truth to the masses. All of his writings, including the link that you provided, are from the 30's, 40's and 50's, so the claims do not reflect advances in the last 50 years.

Thanks for the link. I found it difficult to make my way around there, as the llist of contents are simply labeled as vaolume1, volume 2, etc. with no apparent list of titles. After quite a bit of searching I did find the following:

which, I believe simply confirms what I posted, namely that recent radiocarbon dates should be suspect because the local variations in the use of fossil fuel.

With that being said, I would like to point out that I am not a creationist, nor do I suscribe to Velikovsky's explanations for catastrophic events. I do, however, find his reconstruction of Egyptian and Near Eastern history facinating and do believe that catastrophic events, such as Santorini played a major role in shaping history.

Thanks to all for the information on carbon dating. Here's a website that discusses how the controlling board of D. O. Jerez uses the technique:

Aged Dated Sherry – Since the year 2000, the controlling board of the D.O. Jerez, known as the Consejo Regulador, has approved a category of 20 and 30 year old certified wines. To become certified, the sherries have to go through a lengthy approval process which is carried out by an independent panel of Sherry experts. Among other requirements, a carbon dating sample is taken to ensure that the youngest molecules of wine in a given solera exceed the 20 or 30 year old age minimum.

Something sounds wrong about this approach; if I understand the contributions here, the dating is done by comparing the ratio of two types of carbon molecules. Wouldn't there always be C12 carbon molecules in the sample?

Howie, There are techniques in use to account for possible fossil fuel induced C14 variation in biological materials. The article in question relates to work aimed at indirectly quantifying the effect of atmospheric fossil fuels on the levels of C14 and other isotopes. Radiocarbon dating is certainly not a perfect tool for determining the age of relatively recent materials. It should be one of several tools that are used to determine the veracity of a claimed age.

We come at Velikovsky from different perspective. In my opinion he was a crank with a clear agenda, at least in terms of his work in geology and world history. Whenever I hear claims of conspiracy my "charlatan" alarm goes off immediately. I am not familiar with is work in other disciplines.

Now, pour yourself a nice glass of "Evolution" and enjoy.

Sam

"The biggest problem most people have is that they think they shouldn't have any." - Tony Robbins

Let me explain why the C14/C12 ratio in the latter 20th century is distorted from previous epochs that are within reach of the carbon dating technique.

The amount of CO2 in the atmosphere now is at least 50% higher than ever measured before. That means that more C14 is being produced in the atmosphere now (and in the recent decades) than in the previous few mellennia.

It is necessary to understand that the fossil fuels themselves do not contribute C14. But the C12 they contain goes into the atmosphere when burned, and cosmic rays convert a small fraction to C14. Since there is more C12 in the atmosphere - and given a constant rate of conversion to C14 - this causes more C14 (a higher concentration) than is normal.

I think the italic statement by Howie is wrong. 20th century lifeforms will appear to be younger (high C14 ratio) than would be expected given the ratio of prior centuries. The implication is that (without historical correction), scientists in 1000 years could be befuddled by an apparent gap between life from 20th century on and that before. If scientists in the future assume that the proper calibration is to a higher ambient C14 ratio (as it is now), then it would appear that pre-20th century lifeforms were older than they really are.

Bernard Roth wrote:Let me explain why the C14/C12 ratio in the latter 20th century is distorted from previous epochs that are within reach of the carbon dating technique.

The amount of CO2 in the atmosphere now is at least 50% higher than ever measured before. That means that more C14 is being produced in the atmosphere now (and in the recent decades) than in the previous few mellennia.

It is necessary to understand that the fossil fuels themselves do not contribute C14. But the C12 they contain goes into the atmosphere when burned, and cosmic rays convert a small fraction to C14. Since there is more C12 in the atmosphere - and given a constant rate of conversion to C14 - this causes more C14 (a higher concentration) than is normal.

I think the italic statement by Howie is wrong. 20th century lifeforms will appear to be younger (high C14 ratio) than would be expected given the ratio of prior centuries. The implication is that (without historical correction), scientists in 1000 years could be befuddled by an apparent gap between life from 20th century on and that before. If scientists in the future assume that the proper calibration is to a higher ambient C14 ratio (as it is now), then it would appear that pre-20th century lifeforms were older than they really are.

You've got it backwards because the amount of stable C12 has increased. C14 is not created from C12, but Nitrogen, N14 in the atmosphere, which remains relatively constant.

There are three principal isotopes of carbon which occur naturally - C12, C13 (both stable) and C14 (unstable or radioactive). These isotopes are present in the following amounts C12 - 98.89%, C13 - 1.11% and C14 - 0.00000000010%. Thus, one carbon 14 atom exists in nature for every 1,000,000,000,000 C12 atoms in living material. The radiocarbon method is based on the rate of decay of the radioactive or unstable carbon isotope 14 (14C), which is formed in the upper atmosphere through the effect of cosmic ray neutrons upon nitrogen 14. The reaction is: